Interaction

In this article, we’ll see how to interact with our 3D scenes using a technique called picking. Picking helps us answer the question “What did the user just tap on?” More precisely, picking is the process of determining which object or objects in our scene are being indicated by an interaction like a mouse click or a touch on the screen. Picking is frequently used in 3D modeling and CAD programs to select objects for further manipulation, but many applications eventually require the user to interact with the scene, and picking is an essential tool for enabling such interactions.

Picking is mostly synonymous with hit-testing, which is the more commonly-used term when discussing 2D graphical user interfaces. In fact, you may already be acquainted with UIKit’s model for hit-testing. For the purposes of this article, picking and hit-testing are identical.